The present invention provides an apparatus and method for dispensing a slurry and facilitates the prevention of scaling or sedimentation in feed lines. While specific problems encountered in the dispensing of a lime slurry are discussed, the invention should be understood to apply to the dispensing of slurries generally.
Slurries are used industrially for a variety of applications. By way of example, the physical properties of slurries may be utilized for polishing various industrial surfaces. Alternatively, chemical properties of a slurry may be important in applications such as waste treatment or water purification. In general terms, slurries are created by mixing solids, such as a powder, with liquids. While solvation may occur, typically slurries include particles of a solid suspended or present throughout the liquid phase.
The presence of the solid particles typically associated with slurries creates numerous processing challenges, particularly with pumping and flow through piping. For example, solid particles from the slurry may be abrasive and prone to settling out of the liquid phase when not constantly agitated or maintained at certain minimal velocities in processing systems. Abrasiveness can cause excessive wear on the components of a particular process. The settling out of various particles can clog piping as well as various instruments and components of a piping system.
Because of the abrasive nature of a typical slurry, positive displacement pumps are frequently utilized for pumping operations. Compared to other type of pumps available, positive displacement pumps offer enhanced pump life when using abrasive slurries. An undesirable consequence, however, of utilizing positive displacement pumps for the delivery of slurry is frequently a pulsing output pressure and/or velocity. The fluctuating changes in pressure and velocity may frequently result in undesirable settling of solid particles. This problem may be exacerbated as the diameter of output piping is decreased or the length of travel between the positive displacement pump and delivery point is increased. Furthermore, a back pressure generally must be maintained against a positive displacement pump to ensure its proper operation. Otherwise, slurry may be undesirably siphoned through the pump or clogging of the pump may occur.
Lime is a substance having a variety of useful applications. For example, as set forth in U.S. Pat. No. 5,277,491, which is incorporated in its entirety herein by reference, lime may be used to treat drinking water and waste water. The addition of lime can increase the alkalinity of water that has an undesirably low pH. Frequently, slurries created with lime and water are used for the delivery and application of the lime. Such lime slurries offer material handling challenges in addition to those discussed above with regard to slurries generally.
For example, to maintain a back pressure against a positive displacement pump being used to meter a slurry, a fluid such as water may be introduced under pressure at or near the discharge of the pump. While water under pressure can maintain the desired back pressure against the pump, with lime slurries undesirable scaling or calcification may occur as the water reacts with the lime in the slurry from the pump. The amount and rate of scaling will vary depending upon the pH and content of the water and lime slurry being used. For some applications, periodic maintenance may be required to remove the scale from certain equipment such as the piping or tubing being used to delivery the slurry. In addition, due to the possibility of problems with scaling, calcification, or other build-up, it was previously believed that piping or tubing with diameters smaller than approximately xc2xe inches could not be used without undue problems. Undesirable limitations on the lengths of piping or tubing to transport lime slurry were also observed in an effort to minimize the effect of the build-up.
In accordance with one form of the present invention, there is provided an apparatus or process for delivery of a slurry. In certain embodiments, the present invention allows for slurry delivery over greater distances and allows the use of piping or tubing having smaller diameters than was previously believed acceptable. By way of example only, with the present invention, piping and tubing diameters of approximately xe2x85x9cxe2x80x3 have been successfully tested with lime slurries. In addition, feed lines over 800 feet long have been successfully tested for lime slurries with the present invention. The frequency of maintenance previously required to remove buildup in equipment has been substantially reduced or even eliminated.
In accordance with one exemplary embodiment of the invention, a tank is provided for receiving the slurry. The tank has an outlet for release of the slurry and an agitator associated with the tank for providing agitation to the slurry. A conduit is provided in fluid communication with outlet of the tank and is used for delivering slurry from the tank to a pump. The slurry is pumped from the tank to a flexible member that has an interior surface in contact with slurry passing through the flexible member. The flexible member also has an exterior surface. The flexible member is located in a housing and together the flexible member and housing form a chamber for the receipt of a gas. The chamber receives gas for applying a pressure upon the exterior surface of the flexible member. The pump may be a positive displacement pump. The conduit may be inclined upwardly from the outlet of the tank to help maintain agitation of the slurry in the conduit. More specifically, the conduit may be inclined at an angle of at least 30 degrees from horizontal. Rubber may be used as a material of construction for the flexible member.
In another exemplary embodiment of the present invention, a vessel is provided that contains a slurry. The vessel has an opening for the flow of the slurry from the vessel to a pump. The pump has an inlet and an outlet. Means are provided in fluid communication with the pump and are adapted for using a gas to apply a pressure against slurry flowing from the outlet of the is pump. A conduit may be connected to the opening of the vessel to connect the vessel to the inlet of the pump. The conduit may be inclined upwardly from the opening of the vessel. An agitator may be provided with the vessel for agitating the contents of the vessel.
In still another embodiment, a tank is provided for receipt of the slurry. The tank has an upper portion and a lower portion. A lower portion has an outlet which is connected to a pump by a conduit. The conduit has an initial portion that is inclined upwardly from the point where the conduit connects to the outlet of the tank. An expandable member is provided that is in fluid communication with the pump. The expandable member has an interior surface forming a channel through which slurry flows and also has an exterior surface. The expandable member is configured so as to provide a back pressure on slurry being delivered from the pump. The expandable member may be received into a housing so as to form a chamber between the housing and the expandable member. Gas may be held in the chamber and used to apply pressure to the exterior surface of the expandable member. Means may be provided for monitoring the pressure of the gas in the chamber, and the tank may be equipped with an agitator for agitating the contents of the tank. Such agitator may include one or more propellers. The conduit may have a portion that is inclined upwardly from the outlet of the tank at an angle of at least 30 degrees or more from the horizontal.
In another embodiment of the present invention, there is provided a process for delivering a slurry. The process includes applying slurry to a pump. The pump has an inlet and an outlet. Slurry is discharged from the outlet of the pump to a flexible element that expands or contracts so as to provide a back pressure against the slurry discharging from the outlet of the pump. Pressure may be applied to the exterior surface of the flexible element using a gas. The amount of expansion and contraction of the flexible element due to changes in the slurry being fed through the flexible element may be adjusted by adjusting the pressure of the gas. In certain embodiments, the pump may be a positive displacement pump. Rubber may be used as a material of construction for the flexible element. After feeding the slurry through the flexible element, the slurry may be further transported for treatment, use, or storage.
In still another embodiment of the present invention, there is provided a process for dispensing a slurry that includes agitating the slurry within a vessel having an outlet. The slurry is fed from the outlet of the vessel using a pump that has an inlet and a discharge. The slurry is then pumped to means for using a gas to apply pressure back against the discharge of the pump. The slurry is then delivered to a desired application.
In still another exemplary embodiment of the present invention, there is provided a process for dispensing a slurry from a vessel to a remote location where the slurry may be stored, treated, or applied. The process includes pumping the slurry from the vessel using a pump. The slurry is then fed through a flexible member that is located downstream from the pump and configured for applying pressure to the pumped slurry. The size of the flexible member is then automatically adjusted in order to maintain a back pressure on slurry discharging from the pump. The slurry from the flexible member is then supplied to the remote location. The slurry may be agitated while present in the vessel.
These and other embodiments, features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments, or portions thereof, of the invention and, together with the description, serve to explain the principles of the invention.